1. Field of the Invention
The present invention relates to a decoupling circuit and an antenna device, and more particularly, to a decoupling circuit and an antenna device capable of enhancing isolation of monopole antennas effectively and contributing full use of three-dimensional space.
2. Description of the Prior Art
Electronic products with wireless communication functionalities utilize antennas to emit and receive radio waves, to transmit or exchange radio signals, so as to access a wireless communication network. Therefore, to facilitate a user's access to the wireless communication network, an ideal antenna should maximize its bandwidth within a permitted range, while minimizing physical dimensions to accommodate the trend for smaller-sized electronic products. Additionally, with the advance of wireless communication technology, electronic products may be configured with an increasing number of antennas. For example, a long term evolution (LTE) wireless communication system and a wireless local area network standard IEEE 802.11n both support multi-input multi-output (MIMO) technology, i.e. an electronic product is capable of concurrently receiving and transmitting wireless signals via multiple (or multiple sets of) antennas, to vastly increase system throughput and transmission distance without increasing system bandwidth or total transmission power expenditure, thereby effectively enhancing spectral efficiency and transmission rate for the wireless communication system, as well as improving communication quality.
As can be seen, a prerequisite for implementing spatial multiplexing and spatial diversity in MIMO is to employ multiple sets of antenna to divide a space into many channels, in order to provide multiple antenna field patterns. When an electronic product is configured with multiple sets of antenna under a limited space, a basic requirement includes that these antennas are independent, do not affect each other, and have good isolation. Therefore, how to reduce mutual coupling between antennas becomes one of the industry goals. However, in the limited space, to enhance the isolation of the antennas and simultaneously maintain throughput of MIMO must increase design complexity. Therefore, it is a common goal in the industry to design antennas that suit both transmission demands, as well as dimension and functionality requirements.